A wellbore can be drilled into a subterranean formation to extract formation fluids such as oil or gas. The wellbore can be drilled using a drill string that can include a bottomhole assembly (BHA), a drill bit, and other components. The wellbore may be a vertical wellbore or a deviated wellbore in which the wellbore is intentionally drilled in a direction other than solely in a vertical direction.
A deviated wellbore can be accomplished by using whipstocks, BHA configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface, mud motors, and drill bits. Drilling parameters such as weight on bit and rotary speed can be used to deflect the bit away from the axis of the existing wellbore.
A bend near the bit in a downhole steerable mud motor can be used in directional drilling. The bend can point the bit in a direction that is different from the axis of the wellbore when the drill string is not rotating. By pumping mud through the mud motor, the bit turns while the drill string does not rotate, allowing the bit to drill in the direction it points. When a particular wellbore direction is achieved, that direction may be maintained by rotating the drill string, including the bent section. Directional drilling can allow drillers to place the wellbore in contact with selected reservoir rock.
The mud motor can include a stator and rotor configuration—the stator being the stationary component and rotor being the component that rotates. The stator can be coupled to other components of the drill string. As the drill string bends, the point at which the stator is coupled to the other components can experience stress and be susceptible to breaking, which can delay drilling and be costly.